This invention relates to a pattern forming technique using a charged particle beam or an electromagnetic wave beam, and more particularly to a pattern forming method and a pattern forming apparatus for positioning a beam of any voluntary shape and repeating shot exposure and butt-joining shots to form a desired pattern.
With the advance of high integration techniques relating to VLSIs and pattern dimension refining techniques, it has been difficult to secure accurate pattern dimensions. In particular, it is considered necessary to keep the dimensions of gate patterns within xc2x110% of the target dimension, in order to restrain variations in the characteristics of a transistor within an allowable range. Further, it is considered necessary to keep a dimension error due to lithography within xc2x17% of the above target dimension. For example, where the gate pattern dimension is 0.15 xcexcm, the allowable dimension error in the lithography process is less than xc2x10.0105 xcexcm.
Consider the case of forming a device pattern by first forming a master mask (a photomask, an X-ray mask, an electron beam mask, an ion beam mask, etc.) for the device pattern using a mask writing tool (which writes a pattern with an electron beam or a laser beam), then radiating the master mask with electromagnetic waves such as light, an X-ray, etc., or with charged particles such as an electron beam, an ion beam, etc. to thereby project an image of the mask on a wafer. In this case, the writing accuracy of the mask writing tool may be a main cause of the dimension error.
In the shot-by-shot exposure processing represented by the electron beam exposure technique, there are known a raster scan system for scanning a constant beam, and a vector scan system for positioning a beam at an individual coordinate to perform exposure thereat. The raster scan system performs beam scanning in an analog manner. In this case, to increase the speed of processing, the speed of beam scanning is increased. If the beam size is reduced in order to enhance the resolution, the speed of processing will inevitably decrease. As a method for realizing higher processing, the vector scan system is proposed, which employs a variable shaped beam and can increase the beam size. In this system, setting of the beam size and positioning of the beam are controlled by digital processing. Accordingly, the throughput and the pattern accuracy depend upon the setting speed of a DAC (digital-to-analog converter) employed therein.
A master mask such as a photomask, etc. requires high accuracy in pattern position and dimension. For example, a photomask for a semiconductor element requires that variations in pattern dimension should fall within a range of about 1/30 or less of a minimum line width, and variations in position should fall within a range of 5% or less of the minimum line width. In addition, further enhancement of accuracy is now required since the size of a semiconductor element has been reduced to 70% in every three years.
It is the object of the invention to provide a pattern forming method and a pattern forming apparatus, which use position information concerning an area requiring high dimension accuracy in order to realize high writing accuracy.
According to a first aspect of the invention, there is provided a method of forming a pattern for a semiconductor device, comprising:
the step of forming a photosensitive film on a substrate; and
the step of radiating the photosensitive film on the substrate with a beam of a predetermined shape obtained from one of a charged particle beam and an electromagnetic beam, thereby forming an exposed region of a desired shape, the step including the step of exposing each of unit regions by a single shot of the beam of the predetermined shape for a predetermined period of time, repeating the exposure a plurality of times, and butt-joining the exposed unit regions to thereby form the exposed region of the desired shape;
wherein, in the step of forming the exposed region of the desired shape, butting portions of the unit regions are situated in a first area of a layer to be formed other than a second area of the layer in which predetermined characteristics of a function of the semiconductor device are determined by a pattern width of the exposed region in association with another pattern formed in another layer.
Preferably, the first area in which the butting portions of the unit regions are situated corresponds to an isolation region employed in the semiconductor device.
More preferably, the second area in which the predetermined characteristics of the predetermined function are determined by the pattern width of the exposed region corresponds to an active region incorporated in a transistor in the semiconductor device.
Also preferably, the region in which the predetermined characteristics of the predetermined function are determined by the pattern width of the exposed region corresponds to an electrode region to which an interlayer contact in the semiconductor device is connected.
The step of forming the photosensitive film on the substrate may use a positive-type photosensitive material or a negative-type photosensitive material.
According to a second aspect of the invention, there is provided a method of forming a pattern comprising:
the step of forming a photosensitive film on a substrate; and
the step of radiating the photosensitive film on the substrate with a beam of a predetermined shape obtained from one of a charged particle beam and an electromagnetic beam and emitted from a writing tool, thereby forming an exposed region of a desired shape, the step including the step of exposing each of unit regions by a single shot of the beam of the predetermined shape for a predetermined period of time, repeating the exposure a plurality of times, and butt-joining the exposed unit regions to thereby form the exposed region of the desired shape;
wherein the step of forming the exposed region of the desired shape includes the step of subjecting predetermined ones of the unit regions to single shot exposure, and subjecting the other ones of the unit regions to multiple shot exposure.
Preferably, in the step of forming the exposed region of the desired shape, the multiple shot exposure is performed by repeating the same shot exposure in the same position.
Alternatively, in the step of forming the exposed region of the desired shape, the multiple shot exposure is performed by changing the butting position of the unit regions in units of a single shot exposure treatment.
Alternatively, the step of forming the exposed region of the desired shape selectively uses multiple shot exposure in which the same shot exposure is repeated in the same position, and multiple shot exposure in which the butting position of the unit regions is changed in units of a single shot exposure treatment.
The step of forming the photosensitive film on the substrate may use a positive-type photosensitive material or a negative-type photosensitive material.
Preferably, the step of forming the photosensitive film on the substrate includes the step of using a combination of manners of optical overlap of first and second apertures employed in the writing tool to form the beam of the predetermined shape, and the same combination of the manners of optical overlap of the first and second apertures is used at the time of subjecting to single shot exposure those of the unit regions which have the same shape.
According to a third aspect of the invention, there is provided an apparatus for forming a pattern for a semiconductor device, comprising:
beam shaping means for shaping, to a predetermined shape, one of a charged particle beam and an electromagnetic beam;
positioning means for positioning the position of the beam of the predetermined shape in a single unit region of a substrate with a photosensitive film formed thereon; and
shot exposure means for radiating the single unit region with the beam for a predetermined period of time;
wherein the shot exposure means repeats shot exposure in units of a single unit region to thereby form a desired exposed region; and
the positioning means sequentially forwards the position in which the beam is to be radiated, butt-joins the single unit region to another single unit region to form a plurality of butt-joined unit regions, and situates butting portions of the butt-joined unit regions constituting the desired exposed region, in a first area of a layer to be formed other than a second area of the first layer in which predetermined characteristics of a function of the semiconductor device are determined by a pattern width of the exposed region in association with another pattern formed in another layer.
The positioning means can cause the second area in which the butting portions of the unit regions are formed, to correspond to an isolation region employed in the semiconductor device.
The positioning means determines the position of the beam such that the second area in which the predetermined characteristics of the predetermined function are determined by the pattern width of the exposed region corresponds to an active region incorporated in a transistor in the semiconductor device.
The positioning means determines the position of the beam such that the second area in which the predetermined characteristics of the predetermined function are determined by the pattern width of the exposed region corresponds to an electrode region to which an interlayer contact in the semiconductor device is connected.
According to a fourth aspect of the invention, there is provided an apparatus for forming a pattern comprising:
beam shaping means for shaping, to a predetermined shape, one of a charged particle beam and an electromagnetic beam;
positioning means for positioning the position of the beam of the predetermined shape in a single unit region of a substrate with a photosensitive film formed thereon; and
shot exposure means for radiating the single unit region with the beam for a predetermined period of time;
wherein the shot exposure means subjects predetermined ones of the unit regions to single shot exposure, and the other ones of the unit regions to multiple shot exposure, and the positioning means sequentially forwards the position in which the beam is to be radiated, and butt-joins the single unit region to another single unit region to form a plurality of butt-joined unit regions.
Preferably, the shot exposure means performs the multiple shot exposure by repeating the same shot exposure in the same position.
More preferably, the shot exposure means performs the multiple shot exposure by changing the butting position of the unit regions in units of a single shot exposure treatment.
The shot exposure means may perform the multiple shot exposure by selectively using multiple shot exposure in which the same shot exposure is repeated in the same position, and multiple shot exposure in which the butting position of the unit regions is changed in units of a single shot exposure treatment.
In the pattern exposure method for setting the size of a beam shot and the position of the beam shot by means of digital processing, it is known that a pattern formed by single shot exposure is superior, in principle, in dimension accuracy to a pattern formed by multiple shot exposure. Specifically, pattern portions formed by different shot exposure treatments have variations in dimension accuracy and position accuracy. In the case of a pattern formed by multiple shot exposure, pattern portions formed by different shot exposure treatments may well overlap each other, thereby reducing the accuracy of dimension. On the other hand, in the case of forming each portion of a pattern by repeating the exposure of the same shot, the position accuracy of each portion is averaged, with the result that the pattern accuracy more limited by position accuracy than by shot dimension is enhanced. Such an averaging effect contributes to enhancement of the accuracy of a region formed of an unexposed portion.
Application of the present invention will enhance particular accuracy of a particular pattern portion. For example, in manufacturing a semiconductor element, high accuracy is required for the dimension of a limited portion such as the dimension of a particular pattern, the dimension of a particular portion of a particular pattern, or the distance between particular portions of patterns.
Thus, the accuracy can be enhanced by applying the present invention to a pattern having portions formed by regularly repeating single shot exposure, or by applying the present invention to an extracted particular portion of a pattern. More specifically, a pattern portion which should be limited by a single shot width is subjected to single shot exposure, while other pattern portions are subjected to multiple shot exposure. In this case, the multiple shot exposure portion can obtain high accuracy in the dimension between pattern portions or in the position of each pattern portion, and the single shot exposure portion can obtain high accuracy in the dimension of the shot width.
Moreover, subjecting a peripheral portion of a selected unexposed portion to multiple shot exposure can enhance the accuracy of the dimension of the unexposed portion without significantly reducing the throughput. In addition, the present invention enables exposure of a particular portion with no butting portions, thereby enabling forming of a pattern with little edge roughness and remarkable accuracy of dimension.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.